In the casting of molten metals such as aluminum, apparatus and processes have been developed for the simultaneous casting of a plurality of logs, billets or round ingots, hereinafter logs, so as to increase the efficiency and productivity of the casting process. In such processes and apparatus, a casting table having a plurality of apertures or molds is mounted over a pit from which emerge an equally numbered plurality of hydraulically operated bottom blocks. Each of the bottom blocks is registered, i.e. aligned with, one of the molds or apertures. The casting table includes trough or distribution channels for the dissemination of molten metal introduced into thereto to each of the individual molds or apertures located in the casting table. As metal from the distribution channels or troughs in the casting table enters the individual molds, the plurality of bottom blocks is lowered in unison to allow for removal of metal that has solidified in the mold therefrom and to provide space for the introduction of additional incoming molten metal. Water is sprayed at carefully selected points below the molds or apertures to assist in the solidification of the molten metal passing through the mold or aperture. Such a prior art casting table is shown in FIG. 1 and described in greater detail hereinafter.
While the metal distribution of the casting tables of the prior art as depicted in FIG. 1 have proven highly useful and reliable over many years of service in a multitude of installations, they suffer a number of shortcomings.
As those skilled in the metal casting arts are well aware, it is critically important that molten metal reach each of the molds or apertures at substantially the same time with minimal temperature loss to obtain a successful cast of the plurality of logs being simultaneously cast. If metal reaching one or more apertures is too hot or hold time is too short and does not solidify as the bottom clock or base plate descends, a “bleedout” can result. In such a condition, molten metal can be brought into contact with water applied as a spray in the process of cooling the solidifying metal. Such a condition requires rapid plugging of the aperture or mold that is experiencing the “bleedout” with the result that that portion of the production is lost for the cast. Alternatively, if metal has resided in the mold for too long a period of time, it may be cooler that the balance of the molten metal and therefor solidify more quickly in the cooler mold than metal entering other molds in the casting table resulting in a “freeze-in”, i.e. the solidified metal becomes caught in the mold. A freeze-in can drop out during casting and also result in a bleedout. Such a condition can result in the aborting of the cast entirely and necessitate a free up of the metal caught in the mold and a restart of the cast. Such errors cause significant productivity losses and, more importantly, place operators in significant danger from a safety standpoint. If metal enters the mold with too much velocity or too hot, penetrates between the mold and the soldified head of the forming log “flashing” may occur. Flashing is another condition that may result in molten metal coming into contact with cooling water applied to the log below the solidification point. Flashing also causes damage to molds or distortion or delays in the bottom block movement that can also result in casting defects, bleedouts or complete table freeze-in that requires abortion of the cast and an extensive and time consuming clean up.
Finally, the mold portions of the prior art casting tables comprise multi-part elements that require assembly in the casting table costing valuable assembly or set-up time and which because of their design leave exposed joints between the individual elements of the assembly that are sometimes prone to leaking, particularly if not carefully and properly assembled.
From the foregoing and as well known to those skilled in the molten metal casting arts, control of the temperature of the molten metal from the time that it enters the molten metal distribution system until it pass through one of the molds is critically important to the successful practice of molten metal casting. Hence, minimization of heat loss throughout the process is a primary concern along with ease of set-up.
U.S. Pat. No. 6,848,497 issued Feb. 1, 2005 copending and of common ownership herewith, describes an integral molten metal casting insert comprising a generally cylindrical crossfeeder having and interior surface, a cylindrical thimble having and interior surface of a second diameter and integral back-up insulation all formed as a monolithic structure with the cross feeder interior surface and the thimble interior surface comprising a joint free and uninterrupted cylindrical insert surface peripherally surrounded by the back-up insulation. This patent is incorporated wherein in its entirety for purposes of its disclosure. In this patent, the cross feeder and thimble interior surfaces preferably comprise a low density refractory material and the back-up insulation comprises a castable refractory. More specifically, the low density refractory comprises a fiber glass fabric impregnated with a wollastonite slurry while the castable insulating refractory preferably comprises a phosphate bonded mineral foam composed primarily of calcium silicate. While such a device provides excellent results in terms of solving the potential molten metal leakage problems addressed in that application, as well as the conservation of heat and thus maintenance of temperature referred to herein, it has now been found that difficulty in manufacturing as well as insert life posed previously unforeseen problems. Thus a need has arisen to find a more manufacturable and durable casting insert structure that provides the excellent temperature retention properties of the structure disclosed in the '497 patent while simultaneously avoiding the potential leakage problems of the prior art structures. Similar heat conservation, durability and maintenance issues exist with virtually any molten metal handling system such as transfer troughs etc.